As Usain Bolt and Yohan Blake made their first appearance on the track, Phelps made sure of his 18th Olympic title — and 22nd medal overall — in the 4x100m medley relay, the climax to races in the Aquatics Centre pool.

But the night’s biggest roars were reserved for Ennis, who confirmed heptathlon gold with a surging 800m win that had the 80,000-capacity Olympic Stadium crowd on its feet in a spine-tingling ovation.

As Ennis basked in the stadium applause, Britain’s Greg Rutherford was a surprise winner in the long jump. And Mo Farah then sent the crowd into delirium when he won the 10,000m race.

In the pool “Baltimore Bullet” Phelps, swimming the butterfly leg, made up more than half-a-second over his second 50m as he reeled in front-runners Japan. Nathan Adrian finished the job with an explosive freestyle finish.

The race closed the greatest swimming career in Olympic history, after Phelps’ unmatched eight gold medals at Beijing 2008. In London, he outstripped Soviet gymnast Larisa Latynina as the most decorated Olympian.

Earlier, Sun Yang took more than three seconds off his own 1500m world record to seal China’s fifth swimming gold — making it their most successful Olympics in the pool.

Sun, who flirted with a shock disqualification when he dived in well before the rest of the field, smashed the water repeatedly and cried tears of joy after the race, before getting out and bowing to the stands.

Dutch speedster Ranomi Kromowidjojo completed a sprint double with victory in the women’s 50m freestyle, and Missy Franklin led the United States to a 4x100m medley gold in a world record time of 3min 52.05sec.

The win meant the United States finished on 16 swimming golds, including four for the 17-year-old Franklin, their newest superstar.

South Africa’s Oscar Pistorius became the first double amputee to compete in Olympic track athletics as he sprinted into the 400m semis on his specially made, carbon-fibre blades.

And Serena Williams made tennis history as the first woman to win the ‘Golden Slam’ — all four Grand Slam titles, plus Olympic gold — in both singles and doubles, with a thumping 6-0, 6-1 win over Maria Sharapova.

Defending 100m champion Usain Bolt clocked 10.09sec in his first round heat for the blue riband event of the Games while Jamaican compatriot Yohan Blake timed 10sec.

However, both men were upstaged in front of 80,000 people at the Olympic Stadium by the 9.88sec run by America’s Ryan Bailey.

“I expected it, I’m running well, I’m happy, training is great. Reaction was good,” said Bolt, whose build-up to the Games had been hit by a number of worrying niggles.

South Africa’s Pistorius marked his landmark occasion by qualifying for the 400m semi-finals with a season’s best of 45.44sec.

Pistorius had both legs amputated below the knee before he was aged one, because of a congenital condition, and runs on carbon fibre blades.

“It’s just an experience to be here. It’s a dream come true,” said Pistorius, whose time was the 16th fastest overall.

Defending champion LaShawn Merritt, who has struggled back from a doping ban, stopped running after 250 metres of his heat and crossed the line at walking pace.

On the busiest day so far, with 25 golds to be won, Britain moved into third place in the medals table after two more golds were secured in rowing.

Britain also smashed the women’s team pursuit cycling world record — for the third time this week — to claim their fourth gold out of five so far in the Velodrome, leaving them on course to match their Beijing haul of seven.

In badminton, Li Xuerui took the women’s singles title before Chinese compariots Zhao Yunlei and Tian Qing claimed the women’s doubles.

And former 100m world champion Kim Collins was axed from St Kitts and Nevis’s Olympic squad on Saturday in a row over conjugal visits.

“Even men in prison get their wives to visit,” the 2003 world 100m champion said.

The women’s 100m gold will be the final race decided in Saturday’s evening session at Olympic Stadium.